Quick Office is a Mobile Office Suite for the iPhone. It has the functionality of three different applications in one and is by far the most developed and well thought out application of its kind for the iPhone. The app allows users to experience enterprise-grade Microsoft® Word and Excel® Office functionality with unparalleled ease-of-use.
With QuickWord, users can edit Microsoft Word files with all the standard functions of a word processor. Fonts can be changed and manipulated, bullet points can be added, and even the almighty copy and paste is available. QuickOffice supports pinch zooming and dynamically reformats the text as you zoom. Cursor placement is handled by zooming the entire screen instead of giving a magnifying glass which I found to be extremely handy.
There is also Quicksheet. Quicksheet allows users to edit spreadsheets right from their iPhone or iPod Touch. Calculations are made just like Excel and all the basic functions of Excel are found right in the app. Perhaps the most useful feature in this application is that it allows for syncing documents via wifi. If connected to wifi, the device will generate an URL that can then be accessed via a web browser. Users can then upload any documents they would like to their device for later viewing or editing. The app also supports mounting the device as a wireless drive and using drag and drop to transfer. My largest complaint about the software is it doesn't support iWork 09 files and that iWork files can't be transferred via wifi. But other than that and a few small complaints, this app is amazing.
Each piece can be purchased separately if desired, but for the full feature set, I suggest getting QuickOffice. This is not an app to be casually bought as it will set users back quite a bit in terms of money. But the app well justifies the price if this kind of functionality is what you are looking for.